Summary:
1. Windstorm disturbances create a wide range of microsites which can
have complex effects on forest regeneration patterns. We investigated
the combined effects of light and microtopography on emergence, mortality
and size of seedlings of two bottomland hardwood canopy tree species,
Quercus michauxii and Liquidambar styraciflua, over a 2-year
period. A split-plot design in experimental tanks represented the range
of light levels and the pits and mounds found in a disturbed floodplain
forest.
2. Emergence was always higher on mounds than in pits, except for L.
styraciflua in full sunlight. For both species, mortality was consistently
lower, and seedlings of both species grew better in both years on mounds.
Light levels did not affect the two later stages.
3. There were species-specific interactions between the effects of two
factors on seedling emergence. Lower emergence of L. styraciflua
on mounds in full sunlight suggested that full sunlight at this stage
can eliminate the advantage to later stages of being on a mound. The combined
stresses of low light and a high water table significantly reduced emergence
of Q. michauxii in pits at low light.4.
Microsites optimal for one regeneration component of a species were not
always optimal for others as seen for L. styraciflua. The relative
significance of environmental factors also varied with regeneration stages,
such that neither light nor a light-water interaction influenced regeneration
after emergence.5.
Environmental factors may have independent or interacting effects on regeneration,
and the nature or presence of these effects can vary among demographic
stages. Within each environmental combination, effects may be consistently
positive or negative across stages; alternatively, demographic conflicts
may develop.